Typically, with an inkjet printing apparatus, unevenness such as density unevenness or streaks may be generated in a printed image. The unevenness is caused by shapes of inkjet nozzles or a non-uniform water-repellent treatment. Accordingly, prior to actual image printing, dotted image data is printed for tests. The dotted image data is obtained by performing screening processing based on a plurality of dotted patterns with different density levels. Then, densities of the dotted image patterns printed for tests are determined, whereby nozzle shading correction is performed to a plurality of inkjet nozzles. Here, a variation in ink density occurs also during image printing, which may lead to impossible suppression of the unevenness. Consequently, an inkjet printing apparatus has been suggested that ensures to suppress unevenness in such a case above. See, for example, Patent Literature 1: Japanese Patent Publication No. 2004-106248A.
Patent Literature 1 discloses an apparatus having a pattern recorder, a density measuring unit, and an ink discharge corrector. The pattern recorder records test patterns in an external printing area of inkjet nozzles. The density measuring unit measures densities of the test patterns recorded by the pattern recorder. The ink discharge corrector corrects a discharge amount of ink droplets from each of the inkjet nozzles based on the measured values of the densities by the density measuring unit.
The apparatus having such a construction prints the test patterns prior to actual image printing, and reads the densities of the test patterns. Thereafter, the apparatus performs shading correction to the image data. Accordingly, actual printing is performed while a discharge of amount of ink droplets from each of the inkjet nozzles is corrected. In other words, the correction is made based on the densities immediately before the printing. This ensures to suppress unevenness in the printed image.